L-glutamic acid has been produced by fermentation mainly using so-called coryneform L-glutamic acid-producing strains belonging to the genus Brevibacterium, Corynebacterium or Microbacterium or mutants thereof (Amino-Acid Fermentation, Gakkai Shuppan Center, pp. 195-215, 1986). The other known methods of producing L-glutamic acid by fermentation use microorganisms belonging to the genus Bacillus, Streptomyces or Penicillium (U.S. Pat. No. 3,220,929), and microorganisms belonging to the genus Pseudomonas, Arthrobacter, Serratia or Candida (U.S. Pat. No. 3,563,857). The L-glutamic acid productivity is remarkably increased by the conventional methods. However, in order to meet foreseen increased needs in the future, the development of a more inexpensive and efficient method of producing L-glutamic acid has been in demand.
There is a possibility that bacteria of the genus Escherichia will be used as excellent L-glutamic acid producing-strains in the future because of its high growth rate and advanced gene analysis. It has only been reported so far that a mutant of wild type strain Escherichia coli W, results in accumulation of L-glutamic acid in small amounts of about 2.3 g/liter (J. Biochem., vol. 50, pp. 164-165, 1961). However, recently, it has been shown that a mutant of Escherichia coli K-12, in which .alpha.-ketoglutaric acid dehydrogenase (hereinafter abbreviated as ".alpha.-KGDH) activity is deficient or reduced, exhibits high L-glutamic acid productivity [Japanese Laid-Open Patent Application (Kokai) No. 244,970/1993]. Wild type strains belonging to the genus Escherichia include strains having properties which are better than those of Escherichia coli K-12 and mutants thereof. For Example, it has been reported that Escherichia coli B exhibits higher growth rate than Escherichia coli K-12 and mutants thereof and gives a high yield of biomass based on glucose consumed (J. Biotechnology, vol. 2, pp. 191-206, 1985; and Appl. Environ. Microbiol., vol. 56, pp. 1004-1011, 1990).
It is an object of the present invention to provide an inexpensive and efficient process for producing L-glutamic acid by propagating L-glutamic acid-producing strain which belongs to the genus Escherichia.